The main problem for the methodology indicated by this invention is the precision of the on-line SOC determination and SOH evolution. The measurement of battery voltage is an unsuitable parameter to establish a good correlation with the battery SOH. It is known that the only reliable process to detect premature capacity failures in batteries is the discharge test at a constant current and a specific voltage. However, this method is expensive, requires a lot of time and cannot be implemented for dynamic management.
SOC and SOH determination of batteries subject to different discharge cycles, have been widely used in the last two decades for the research of battery component/unit kinetics. In these previous studies, like “A review of impedance measurements for determination of the state-of-charge or state-of-health of secondary batteries”. F. Huet. Journal of Power Sources 70, pp 59-69, (1998), many authors have concluded that impedance methods are a good method to provide a SOC test.
The modulus representations and the phase of said electrochemical impedance in relation to the frequency by means of Bode diagrams are usual in the characterisation of electronic circuits, although the most common representation in the field of batteries is the Nyquist diagram, which relates the imaginary part with the real part of said impedance.
The main common features of the Nyquist diagrams applied to automobile batteries, particularly those of lead-acid are:                an inductive part at frequencies greater than 100 Hz;        a high frequency resistance RHF in the mΩ range being the real part of the impedance at frequencies greater than 100 Hz;        a first and small capacitive loop for frequencies between 0.1 to 100 Hz;        a second and wider capacitive loop for frequencies greater than 0.1 Hz.        
Therefore, the SOC and SOH of batteries subject to different charge-discharge cycles have been characterised in the laboratory by impedance measurements. Some of the parameters extracted from the RHF spectrum, for example, are directly related to the battery SOC. Moreover, the ohmic resistance RHF of the impedance measurement at high frequencies, is a strong parameter that may be included in a dynamic, “on-line” determination, carried out on the vehicle, for the battery safety regions.
A very common study method of properties depending on frequency consists of modelling the unknown system by means of an equivalent electric circuit. In this context, the following publication may be mentioned: “Dynamic modelling of lead/acid batteries using impedance spectroscopy for parameter identification”. P. Mauracher, E. Karden. Journal of Power Sources 67, pp 69-94 (1997).
Methods and devices or systems for a controlled management of batteries appear in patents WO-A-98/53335 regarding a SOH control system of a battery, EP-A-884600, referring to a device and method to control the SOC of a battery and patent WO-A-98/58270 which refers to a method and apparatus to evaluate and classify batteries, based on the application of microcharges or charge micropulses to the battery, making the classification according to the resulting voltage profiles, or portions thereof, taken at the battery terminals.
U.S. Pat. No. 5,773,978 concerns impedance control for a storage battery including a charge circuit coupled to the terminals of a battery to charge it, so that a voltage component is generated in its posts depending on the time it has a peak to peak amplitude, the measuring unit connected to the battery posts including a peak detector to generate an indicative voltage based on the impedance unit output.
All these systems and particularly that described in the last mentioned patent, are not sufficiently suitable for a measurement and eventual later dynamic management in the automobile itself, since to the battery terminals are connected different charges and sources which would also introduce their components in the output signal, as from which impedance should be measured, hindering measurement precision and making it unreliable.